Wood fuel has always been important. Today advanced wood fuel in the form of pellets is an alternative to fossil fuels. A broad range of furnaces can be modified to use wood pellets instead of coal. For a significant part of such furnaces, the wood fuel is burnt as powder. The powder is obtained by milling wood pellets, but can also be made just by milling dry wood.
Most wood pellets are so-called “white pellets”, which is made from wood that has been dried to about 10% moisture, grinded, and compressed in pellets mills to pellets of typically 6 or 8 mm diameter, lengths typically from 5-20 mm. These pellets return to the form as wood powder if exposed to water, which is a disadvantage. There is great interest in finding a way to produce hydrophobic wood pellets.
Torrified pellets is one solution for hydrophobic wood pellets. Another solution is pellets made from wood which has been steam exploded. Such pellets are also to a large degree hydrophobic, but not totally.
As the quantity of wood being used as raw material for wood pellets increases, the costs of raw materials may rise. While sawdust used to be the main raw material for wood pellets, today ordinary cellulose chips and pulpwood are being used as raw material for wood pellets. This requires that the use of the wood be done in a way to get the most value out of it.
The present invention represents a way to get increased value for the wood. This is done by separating the hemicellulose from those parts of the wood going to be pelletized, and using the hemicellulose for other products. Furthermore, the resulting material may have additional properties which improve its suitability for uses such as fuels.